The release of the first Tier 1 assessments in the Endocrine Disruptor Screening Program (EDSP) by the U.S. Environmental Protection Agency (EPA) on June 30, 2015, is a significant benchmark in the program since the original List 1 test orders were issued in October 2009. This column explains why.
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Original List 1 Chemicals
The intended purpose of Tier 1 screening was to identify potential interactions of chemicals with three hormonal pathways (estrogen, androgen and thyroid) in the endocrine system. Fifteen of the original 67 List 1 chemicals were subsequently cancelled or discontinued by the respective pesticide registrants. The EPA evaluated data from 11 screening assays (five in vitro and six in vivo), along with other scientifically relevant information (OSRI) comprised of existing toxicology studies and peer-reviewed published literature, and drew preliminary conclusions about the potential of these 52 chemicals to disrupt endocrine functions. The EPA concluded the majority of these List 1 chemicals either didn’t exhibit bioactivity in the screening tests or posed no risk. For those chemicals that showed potential interaction with any of the endocrine pathways, higher-tiered testing has been recommended. Importantly, the EPA noted on the EDSP webpage that “[a] result indicating potential should not be construed as meaning that EPA has concluded that the chemical is an endocrine disruptor.”
The individually published weight-of-evidence (WoE) assessments can be accessed online for the 52 chemicals involved in the Tier 1 screening assessment. The EPA is expected to publish the data evaluation records (DER) for the associated studies soon. The agency summarized its conclusions from the EPA’s Tier 1 WoE assessments as follows:
1. Twenty chemicals showed no evidence of potential interaction with any of the endocrine pathways.
2. Fourteen chemicals showed potential interaction with one or more pathways, but based on the available information, do not pose a risk for endocrine disruption.
3. Eighteen chemicals showed potential interaction with the thyroid pathway, 17 of those also showed potential interaction with the androgen pathway, and 14 showed potential interaction with the estrogen pathway.
To explore further any potential adverse effects on the endocrine system that may be caused by the 18 chemicals categorized in the third group noted above, the EPA recommends the following Tier 2, multigenerational studies across various species for them:
• A comparative thyroid assay for four chemicals found to have potential interaction with the thyroid pathway in mammals;
• The Medaka Extended One Generation Reproduction Test, MEOGRT (Draft Test Guideline OCSPP 890.2200), for 13 chemicals the EPA found to have potential interaction with the estrogen or androgen pathways in wildlife; and
• The Larval Amphibian Growth and Development Assay, LAGDA (Draft Test Guideline OCSPP 890.2300), for five chemicals found to have potential interaction with the thyroid pathway in wildlife.
The EPA hasn’t yet issued its final Tier 2 non-mammalian Office of Chemical Safety and Pollution Prevention test guidelines (890 Series). Public comment on the proposed guidelines closed March 31st. It’s expected that the release of these remaining guidelines will signal the approach of the Tier 2 test orders, which the EPA is likely to issue in 2016. Although a formal public comment period isn’t expected to be opened for the Tier 1 assessments, affected registrants should have the opportunity to respond directly to the EPA regarding WoE assessments and forthcoming DERs.
Discussion
This release of the Tier 1 WoE assessments and the anticipated release of DERs and Tier 2 test guidelines, along with the EPA’s commitment to develop further high throughput assays and computational tools, will greatly influence the prioritization of List 2 chemicals in the EDSP, and the timing of the List 2 test orders. The revised List 2 includes 109 chemicals for Tier 1 screening. As with List 1, List 2 candidates reportedly were selected based on the EPA’s review concerning their possible presence in public drinking water or registration review status within the EPA, and not because of their potential to interfere with the endocrine systems of humans or other species.
